Eclipse

There was a lunar eclipse in the early hours of today.

When the Moon is in the Earth’s umbra (totally in shadow), sunlight cannot reach it directly. Yet it glows with two different colours: red and blue. Both are the result of light that was bent as it passed through the Earth’s atmosphere.

The red, familiar to all, is the light that passed right through the atmosphere after much of the blue had been scattered in other directions to give the blue of the daytime skies. Seen from the Moon, the Sun is blocked and the Earth’s atmosphere appears as a ring of the reddish light of many sunsets.

The blue is more subtle and, to see it, timing is important. For a short time just after entering or before leaving the Earth’s umbra, the Moon’s rim is illuminated by light that passed through the Earth’s ozone layer. Ozone absorbs reddish light but allows bluish light to pass through to give the otherwise reddish moon a soft bluish edge. 

The Moon has just entered the Earth’s umbra and appears reddish with a soft bluish edge in the northeast.